When producing printed circuit boards (hereinafter also referred to as PCBs), it is often common to form printed circuitry on one or both sides of a planar rigid or flexible insulating substrate. Of increased importance today is the manufacture of multilayer printed circuits, the most common types of boards sold today in view of increased operational demands for the products, e.g., personal computers, mainframes and servers, in which such boards are implemented. In these structures the board typically consists of parallel, planar, alternating inner layers of insulating dielectric material and conductive metal. Examples of the dielectric material include fiberglass-reinforced epoxy resin (also referred to in the field as “FR4” for its flame retardant rating), polytetrafluoroethylene (e.g., Teflon, a trademark of E.I. DuPont de Nemours & Company), Driclad (a trademark of the Assignee of this invention, Endicott Interconnect Technologies, Inc.), etc. Formation of the conductive layer circuitry is typically accomplished using known photolithographic processing steps in which photo-resist is applied, selectively exposed and developed, with the resulting circuit pattern remaining on the supporting dielectric, including possibly on opposing surfaces thereof. Several of these layered elements (sometimes referred to as “cores”, possibly including three or more conductive layers and two or more dielectric layers) are then aligned and bonded together using conventional lamination processing in which high temperatures and pressures are utilized. Metals used for such conductive circuit layers include copper, copper alloys, nickel and gold.
The above mentioned cores in turn may be referred to as “power” cores (if the conductive layer is to form a power plane), or by other abbreviated terminology such as “2S1P”, meaning the core includes two signal planes and one power plane (with the appropriate number of dielectric layers to provide insulation, of course). Each multilayered final board may include several cores, in addition to other layers such as “sticker sheets” designed to bond one or more cores together.
It is also common in double-sided and multilayer printed circuit boards to provide conductive interconnections between the various conductive layers of the board. This is commonly achieved by providing metallized, conductive “thru holes” in the board which communicate with the layers requiring electrical interconnection. For some applications, it is desired that electrical connection be made with almost if not all of the conductive layers. In such a case, thru-holes are also typically provided through the entire thickness of the board, in which case these are often also referred to as “plated thru holes”. For these, as well as other applications, it is also often desired to also provide electrical connection between the circuitry on one face of the board to a depth of only one or more of the inner circuit layers. These are referred to as “blind vias”, which pass only part way through the board, as stated. In still another case, such multilayered boards often require internal “vias” which are located entirely within the board's structure and covered by external layering, including both dielectric and conductive. Such internal “vias”, also referred to as “buried vias” are typically formed within a sub-part structure of the final board (such as the aforementioned “core”) and then combined with other layers during final lamination of the board. For purposes of this application, the terms “thru hole” is meant to include all three types of such electrically conductive openings.
To provide the desired circuit patterns for the board, including both internal and external, those in the art have developed a variety of manufacturing sequences, many of which fall into the broad categories of “subtractive” or “additive” techniques. Common to subtractive processes is the need to etch away (or subtract) metal to expose substrate surface in areas where no circuitry is desired. Additive processes, on the other hand, begin with exposed substrate surfaces (or thin common metallization layers for additive electroplate) and build up metallization in desired areas, the desired areas being those not masked by a previously-applied pattern of plating resist material (e.g., also called photo-resist in the printed circuit board field).
Typically, thru-holes are drilled (including mechanically or, more recently, using lasers) or punched into or through the board, as well as within the cores or other sub-parts, if desired, at selected locations. Drilling or punching provides newly-exposed surfaces including hole barrel surfaces and hole peripheral entry surfaces. The dielectric substrate, and the core or sub-part, if used, each comprising a top surface, a bottom surface, and at least one exposed internal hole surface consisting partly or entirely of the dielectric insulating material, is then metallized, generally by utilization of electro-less metal depositing techniques, albeit other deposition processes are also known in the field.
In addition to the above processes, some PCBs must also be designed to accommodate what are commonly referred to as edge connectors. Various types of edge connectors are known in the art and are designed typically for being secured to a corresponding edge of the PCB in order to be electrically coupled to a pattern of circuit elements (e.g., elongated pads) formed thereon. Some edge connectors may be secured to the PCB edge using such members as pins which extend within corresponding edge openings, while a more common form of edge connector is designed for simply being frictionally positioned onto the projecting end of the edge portion. Alternatively, the connector is mounted on a “motherboard” such as within a computer and the PCB edge is then inserted therein. This latter form of connector usually includes therein a plurality of contact elements, e.g., curved blade spring contacts, which slidably engage respective ones of the elongated pads on the board edge during positioning. The result is a strong frictional fit, such that the connector may be later removed for repair, including when repair is desired for the PCB itself, or, if the connector is fixedly positioned such as on the aforementioned “motherboard,” removed from the board after the PCB itself is withdrawn. This fit thus enables facile replacement of the connector. It is also possible to fit more than one edge connector onto a single PCB, including on more than one edge portion thereof. As understood from the following, the present invention is specifically directed to the formation of a multilayered PCB with the ability to make sound and facile connection to an edge connector or the like connecting structure.
The following patents describe various approaches to manufacturing printed circuit boards, including those with extending edge portions designed to accommodate edge connectors such as those described above. Examples of such edge connectors are also shown in some of the patents below.
In U.S. Pat. No. 7,147,480, there is described an approach for connecting a flexible printed circuit board to a conventional (non-flexible) printed circuit board. Patterns on both boards are aligned and connected with each other by soldering. An elongated hole is formed in the vicinity of and along the edge portion in a connecting part of the printed circuit board, and two rectangular holes communicating with the elongated hole are formed at both longitudinal ends of the elongated hole, while two notches for controlling insertion depth are provided at opposing ends of the connecting edge of the flexible printed circuit board. The leading edge portion of the flexible printed circuit board, which is left between the cut portions, is bent downward, and the bent portion is inserted into the elongate hole and the rectangular holes of the printed circuit board to position the flexible printed circuit board, and then the patterns, respectively located on the flexible printed circuit board and the printed circuit board, are connected by soldering.
In U.S. Pat. No. 7,084,355, there is described a multilayer printed circuit board in which micro-cracks or metallic migration is mitigated when a “Resin Fill Plated Through Hole” (RFP) is arranged near the edge thereof. The multilayer printed circuit board includes an inner layer having an RFP, outer layers, RFP lands, and conductor layers. The conductor layers are positioned over the RFP lands and the outer edges of the conductor layers extends outward further than the outer edges of the RFP lands. When the multilayer printed circuit board is heated, a stress is generated in and near the RFP. The conductor layers positioned so as to cover the RFP lands, exert a reaction against the stress to suppress generation of micro-cracks in the multilayer printed circuit board and thereby mitigate metallic migration in the board.
In U.S. Pat. No. 7,048,547, there is described a printed-circuit board which is formed with a front edge having a cutout. A plug is provided with a base body adapted to fit in the cutout and formed with a pair of shoulders bearing flatly on the board at edges of the cutout. A pair of wing-shaped connecting elements project oppositely from the body and lie flatly on the board adjacent the edges of the cutout so that the elements can be soldered to the board to fix the base body in the cutout.
In U.S. Pat. No. 7,036,214, there is described a method of manufacturing a rigid-flexible printed circuit board in which slits for defining two sides of a removing portion are formed in a part of plural resin films, and the plural resin films are stacked and bonded to form a circuit board. Then, a product portion is cut from the circuit board. Before the bonding, a separation sheet is disposed between predetermined adjacent layers of the plural resin films to separate the removing portion from a residual portion of the product portion. Accordingly, while the product portion is cut from the circuit board, the removing portion is separated from the product portion, because the removing portion are defined by the separation sheet, the slits, and a cutting outline of the product portion.
In U.S. Pat. No. 6,966,482, there is described the formation of lands formed on a flexible printed circuit board which are electrically connected with lands formed on a rigid printed circuit board through solder. At this point, solder resist is formed between neighboring two lands on the rigid printed circuit board, and is terminated with a projecting end portion that is interposed between the rigid printed circuit board and the flexible printed circuit board. Accordingly, when surplus solder is extruded onto the rigid printed circuit board, the solder resist can prevent solder bridges from being formed between the lands.
In U.S. Pat. No. 6,986,917, there is described the printing of a solder resist comprising a thermosetting resin on a surface of an insulating board having a conductor circuit. The solder resist is then heat-cured to form an insulating film having a low thermal expansion coefficient. A laser beam is then applied to the portion of the insulating film in which an opening is to be formed, to burn off the same portion for forming an opening, whereby the conductor circuit is exposed. This opening may be formed as a hole for conduction by forming a metal plating film on an inner surface thereof. An external connecting pad is formed to cover the opening. The film of coating of a metal is formed by using an electric plating lead, which is preferably cut off by a laser beam after the electric plating has finished.
In U.S. Pat. No. 6,899,546, there is described a printed circuit board which is provided with an attachment which surrounds surface contacts of the printed circuit board that are to be contacted by a printed circuit board connector that covers the portion of the printed circuit board and edges of the printed circuit board around the surface contacts and includes recesses corresponding to the surface contacts assuring proper connection with contacts of a printed circuit board connector.
In U.S. Pat. No. 6,848,175, there are described various methods and structures for allegedly improving the yield of out-of-plane micro-device structures, including the use of springs and coils. In one method the springs used to form out-of-plane structures are constrained via a tether to avoid bunching and entanglement. The structure, according to the authors, may be used in numerous electronic applications such as filter circuits.
In U.S. Pat. No. 6,818,168, there is described a method that puts a pair of bevels onto an edge of a printed circuit board so that the PCB can be inserted into an expansion slot of a computer. The tool has a bevel wheel, preferably with a bi-laterally symmetrical angle channel shape, that is connected to a carriage. The bevel wheel rolls along the carriage while the bevel wheel is pressed onto the edge of the PCB so as to form the pair of bevels on the edge of the PCB. No material is removed from the PCB while forming the pair of bevels. The bevel wheel is forced upon the edge using a piston that monitors and regulates the pressure applied to the edge of the PCB in order to achieve a preferred height and angular orientation of the pair of bevels.
In U.S. Pat. No. 6,688,897, there is described an electrical edge connector designed for being straddle-mounted on an edge of a printed circuit board and which includes an insulating housing having an elongated groove for mating. A support subassembly is inserted from the opposing side of the housing to expose its portions in the groove.
In U.S. Pat. No. 6,634,561, there is described a small, flat rectangular shaped electronic circuit card, such as one containing non-volatile memory, which has a row of contacts mounted on bottom surfaces of a row of recesses extending along a short edge of the card and an adjacent angled corner. At least one of the recesses opens to the angled corner and the remaining recesses open to the short edge. Two surface contacts are included in at least one of the recesses, while the remaining recesses each contain a single contact.
In U.S. Pat. No. 6,324,067, there is described a PCB and assembly which are suitable for high density mounting of an electronic component. A recess is formed in one part of the PCB and components are received in this recess and are lower than the surface of the PCB. A conductive pad is provided to the bottom of the recess and a connecting terminal and the conductive pad are electrically connected by using a solder ball or a conductive adhesive material. The recess is formed by partially removing one or more layers of plural conductive layers and insulating layers which make up the multilayer PCB.
In U.S. Pat. No. 6,209,195, there is described a surface mount connector that can be used for both single and double-sided PCBs. A telephone may have a PCB with connector access from the bottom of the telephone and keypad activation from the top of the telephone. If a double-sided PCB is used, the connector is mounted to the bottom side of the PCB, while the keypad is mounted to the top. The connector faces away from the PCB to provide access from below the telephone. If a single-sided PCB is used, the connector is mounted to the top side of the PCB, so that the keypad can also be mounted to the top side. The connector is placed, with connector access down, into an opening through the PCB. The connector extends down through the opening with the leads of the connector remaining on the top side of the PCB. The leads of the connector are secured to pads on the top side of the PCB.
In U.S. Pat. No. 6,109,939, there is described a memory card which has a card body having a concavity formed at the forward end thereof in the inserting direction and in which terminals are disposed and projections are formed between the terminals to prevent the terminals from being touched or accessed from outside. A receptacle for the memory card is also disclosed. The memory card has a simple structure designed to positively protect the terminals and easily let out dust or the like from inside, thereby permitting to assure a positive connection with the receptacle.
In U.S. Pat. No. 5,939,789, there is described a multilayer substrate which is fabricated by laminating a plurality of substrates, each comprising an insulation film, a plurality of via holes which pass through the upper surface to the lower surface of the insulation film, a wiring which is provided on the upper surface of the insulation film and the upper surface of the via holes and electrically connected with the via holes, a bonding member which is provided on the lower surfaces of the via holes and electrically connected with the via holes, and a bonding layer which is provided on the upper surface of the insulation film where the wiring is formed and the method of fabrication thereof whereby large cost reduction and high density effect are alleged to be obtained.
In U.S. Pat. No. 5,309,629, methods of fabricating multilayer circuits are presented. In this patent, a plurality of circuit layers is stacked, one on top of the other. At least one of the circuit layers comprises a substrate composed of a polymeric material capable of undergoing bonding such as a fluoro-polymeric based substrate having vias there-through and a circuit comprised of a layer of suitable conductive material. A fusible conductive bonding material (e.g., solder) or a noble metal is applied wherever electrical connections are desired. At least one other of the circuit layers comprises a polyimide circuit (or other high temperature non-fusing polymer circuit, with or without filler or fabric reinforcement) having vias and circuits comprised of a layer of suitable conductive material with a fusible conductive bonding material (e.g., solder) or a noble metal applied wherever electrical connections are desired. Once stacked the circuits are subjected to lamination under heat and pressure to adhere each polymeric substrate to an adjacent polyimide substrate and to diffuse the noble metal or fuse the solder layers together to form an integral multilayer circuit having solid conductive interconnects.
In U.S. Pat. No. 4,872,851, there is described an edge electrical connector for providing electrical connection to contact elements on a printed circuit board wherein torsion contacts are utilized. The contacts, actuated by a vertically moving, slidable member (e.g., a cam plate) and horizontally moving actuator (e.g., a linear cam), resume a normal, twisted configuration to effect such connection with the respective contact elements. Each contact, preferably metallic (e.g., beryllium copper), includes a curvilinear edge segment while each contact element (e.g., plated copper wire) in turn includes a curvilinear contacting surface, these two members thus providing a single point form of contact while assuring effective wiping motion to remove undesirable contaminants, debris, etc. which may be located thereon.
In U.S. Pat. No. 4,026,627, there is described an edge connector with an electrical contact including an angular engagement arm for slidably engaging a conductive surface (a pad on a PCB edge), said arm including a noble metal segment thereon for electrically contacting the surface and means for preventing transfer of material from the arm onto the noble segment. The improvement resides within the material transfer prevention means wherein the means comprises at least one elongated blade having at least one edge thereon, the blade formed so that only the edge slidably engages the conductive surface prior to the noble metal segment contacting the surface.
The present invention represents a new and unique method of forming a PCB with at least one edge portion adapted for being positioned within an edge connector which, when securely positioned to the PCB, will be electrically coupled to one or more conductors (e.g., elongated pads) on the PCB's edge. This method is accomplished in such a manner so as to prevent the incursion of dielectric material or the like onto the conductors during bonding (e.g., by lamination) of two substrates to form the PCB. It is believed that such a method will constitute a significant advancement in the art.